Fiber optic cable having low thermal strain and methods of manufacturing the same

ABSTRACT

A polymer composition is provided. The polymer composition includes a polyolefin, at least 30% by weight of a thermoplastic elastomer, and a filler material. When the polymer composition is formed into an article having a longitudinal axis, the polymer composition has an average coefficient of thermal expansion along a longitudinal axis of less than or equal to 150×10 −6  m/mK as measured from −40° C. to 25° C. Further, the polymer composition has an elastic modulus of less than 3000 MPa as measured using dynamic mechanical analysis (ASTM D4065), and the polymer composition has an elongation at break of greater than 200% along the longitudinal axis (measured according to ASTM D638). An article made from the polymer composition and a cable including the polymer composition are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/811,825, filed on Nov. 14, 2017, which claims the benefit of priorityto U.S. Application No. 62/422,824, filed Nov. 16, 2016, bothapplications being incorporated herein by reference.

BACKGROUND

Some polyolefins have advantageous properties for use as cable jacketingmaterials for a variety of cable types. In particular, these polyolefinshave good flexibility and are able to maintain certain relevantmechanical properties over a range of operating temperatures. Thepolyolefins can be extruded to surround the cable so as to help protectthe interior components of the cable from the environment in which thecable is deployed.

SUMMARY

In one aspect, a polymer composition is provided. The polymercomposition includes a polyolefin, at least 30% by weight of athermoplastic elastomer, and a filler material. When the polymercomposition is formed into an article having a longitudinal axis, thepolymer composition has an average coefficient of thermal expansionalong a longitudinal axis of less than or equal to 150×10−6 m/mK asmeasured from −40° C. to 25° C. Further, the polymer composition has anelastic modulus of less than 3000 MPa as measured using dynamicmechanical analysis (ASTM D4065), and the polymer composition has anelongation at break of greater than 200% along the longitudinal axis(measured according to ASTM D638).

In another aspect, an extruded polymer article is provided. The polymerarticle has a longitudinal axis generally in the direction of extrusion.The polymer article is comprised of a polymer composition that includesa polyolefin, at least 30% by weight of a thermoplastic elastomer, and afiller material. The polymer composition has an average coefficient ofthermal expansion along the longitudinal axis of less than or equal to150×10−6 m/mK as measured from −40° C. to 25° C. Further, the polymercomposition has an elastic modulus of less than 3000 MPa as measuredusing dynamic mechanical analysis (ASTM D4065).

In yet another aspect, a cable is provided. The cable includes at leastone communication element, and a polymeric jacket that surrounds the atleast one communication element. The polymeric jacket is formed at leastin part from a polymer composition including a polyolefin, at least 30%by weight of a thermoplastic elastomer, and a high aspect ratio fillermaterial. The polymer composition is extruded to form the polymericjacket, and the polymeric jacket defines a longitudinal axis generallyin the direction of extrusion. The polymer composition has an averagecoefficient of thermal expansion (CTE) along the longitudinal axis ofless than or equal to 150×10−6 m/mK as measured from −40° C. to 25° C.and an elastic modulus of less than 3000 MPa as measured using dynamicmechanical analysis (ASTM D4065).

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and theoperation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention and,together with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a graphical representation of the coefficient of thermalexpansion as measured for a polymer composition made according to anexemplary embodiment;

FIG. 2A is a scanning electron microscope (SEM) micrograph of a crosssection of a polymer composition taken perpendicular to the extrusiondirection, according to another exemplary embodiment;

FIG. 2B is an SEM micrograph of a cross section of the same polymercomposition as shown in FIG. 2A taken parallel to the extrusiondirection, according to an exemplary embodiment;

FIG. 3A is an SEM micrograph of an etched cross section of the polymercomposition of FIG. 2B, according to an exemplary embodiment;

FIG. 3B is the SEM micrograph of FIG. 3A at a higher magnification,according to an exemplary embodiment; and

FIG. 4 is an illustration of an optic fiber cable in which components ofthe cable include polymer compositions made according to exemplaryembodiments.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION

Referring generally to the figures, various embodiments of a polymercomposition having low thermal strain are provided. The polymercomposition generally comprises a polyolefin, a thermoplastic elastomer,and a high aspect ratio filler. Embodiments of the polymer compositionhave a coefficient of thermal expansion (CTE) in an extrusion directionof less than 150×10⁻⁶ m/mK and an elastic modulus of less than 3000 MPa.In embodiments, the polymer composition can be used to reduce thethermal strain on optic fiber cable components (e.g., outer cablejackets, inner cable jackets, binder layers, etc.) for cables such asloose tube cables, ribbon cables, indoor cables, etc. While embodimentsof the polymer composition are discussed in the context of optic fibercables, such discussion is not intended to limit the possible contextsand applications in which the polymer composition can be utilized.

As mentioned above, the disclosed polymer composition has particularapplicability for reducing the thermal strain in loose tube optic fibercable. One way to express the thermal strain of a loose tube cable isprovided in the following equation:

${ɛ_{T}\left( T_{o} \right)} = \frac{\sum\limits_{Cable}\; \left( {{E_{i}(T)}A_{i}{\int_{T_{a}}^{T_{o}}{{\alpha_{i}(T)}{dT}}}} \right)}{\sum\limits_{Cable}\; \left( {{E_{i}(T)}A_{i}} \right)}$

where, E is a material's elastic modulus, A is a material'scross-sectional area, and a is a material's CTE. As indicated in theequation, the CTE and elastic modulus both influence the thermal strainε_(T) experienced by an optic fiber cable. Thus, in order to reduce thethermal strain on a cable, both the CTE and elastic modulus have to beconsidered in the operating temperature range of the optic fiber cable.However, efforts to reduce the CTE generally have the inverse impact onthe elastic modulus, and vice versa, especially when fillers areintroduced into the polymer composition, which means that the overallthermal strain is not changed. In contrast, embodiments of the disclosedpolymer composition provide a reduced CTE along the cable length whilestill maintaining the elastic modulus such that the thermal strain alongthe cable length is reduced.

In embodiments, the polymeric composition includes a polyolefin, athermoplastic elastomer, and at least one filler material. In exemplaryembodiments, the polyolefin can include one or more of medium-densitypolyethylene (MDPE), high-density polyethylene (HDPE), low-densitypolyethylene (LDPE), linear low-density polyethylene (LLDPE), andpolypropylene (PP). In other embodiments, a different polyolefin canalso be used.

In an embodiment, the polymer composition includes at least 30% byweight of the thermoplastic elastomer. In further embodiments, thepolymer composition includes less than 60% by weight of thethermoplastic elastomer. In other embodiments, the polymer compositionincludes less than 50% by weight of the thermoplastic elastomer, and inadditional embodiments, the polymer composition includes less than 40%by weight of the thermoplastic elastomer. Exemplary thermoplasticelastomers suitable for use in the polymer composition include (but arenot limited to) ethylene-propylene rubber (EPR),ethylene-propylene-diene rubber (EPDM), ethylene-octene (EO),ethylene-hexene (EH), ethylene-butene (EB), ethylene-vinyl acetate(EVA), and styrene-ethylene-butadiene-styrene (SEBS), thermoplasticvulcanizates (TPV [e.g., Santoprene available from ExxonMobilChemical]), polyolefin elastomers (POE), ethylene/alpha-olefincopolymers (e.g., Exact plastomers available from ExxonMobil Chemical)and combinations thereof. In a particular embodiment, thermoplasticelastomer used in the polymer composition has a shear viscosity that islower than or equal to the shear viscosity of the polyolefin whenmeasured at 200° C. and 100 s⁻¹. As will be discussed in more detailbelow, this increases the stability of the highly oriented co-continuousmorphology during extrusion, maintaining the low CTE advantage disclosedherein.

The particles of the filler material used in the polymer compositionhave a high aspect ratio, i.e., a high width to thickness ratio or ahigh length to width ratio. In an embodiment, the particles of fillermaterial have an aspect ratio of 5 or higher. In specific embodiments,the inorganic fillers can be platelike or fibrous/rodlike. Examples ofplatelike fillers include mica, talc, montmorillonite (MMT), kaolinite,bentonite, synthetic clay, and other clays. Examples of fibrous/rodlikefillers include wood flour (WF), glass fiber (GF), halloysite,wollastonite, magnesium oxysulfate, and other reinforced fibers. In anembodiment, the polymeric composition includes less than 30% by weightof the filler material. In a further embodiment, the polymer compositionincludes less than 20% by weight of the filler material, and in stillanother embodiment, the polymer composition includes less than 10% byweight of filler material.

The polymer composition can include other processing and/or performanceadditives. For example, a dispersant and a compatibilizer may be addedto aid dispersion of the inorganic filler, to improve compatibilitiesbetween polymer matrices, and/or to stabilize the phase morphology. Anexemplary compatibilizer would be a block copolymer that has alternatingolefin blocks and one or more other monomer blocks. For example, onesuitable compatibilizer for SEBS is a copolymer with alternating blocksof polyethylene and styrene-containing segments. In another example, thecompatibilizer is a polymer having a polyolefin backbone that is graftedwith a monomer in which the monomer is compatible with the selectedthermoplastic elastomer. Another possible additive for the polymercomposition is carbon black, which can help absorb ultra-violet lightfor outdoor applications of the polymer composition. Still further, thepolymer composition can include up to 1% by weight of a low frictionadditive, such as a fatty acid or a fatty acid amide. For example, thefatty acid can have a carbon backbone of between C₆ to C₂₅ and besaturated or unsaturated. Specific examples include caprylic acid,capric acid, lauric acid, myristic acid, palmitic acid, stearic acid,arachidic acid, behenic acid, lignoceric acid, cerotic acid, etc.Similarly, the fatty acid amid can have carbon backbones, for example,of between C₆ and C₂₅ and be saturated or unsaturated.

In embodiments, the polymer composition is prepared via extrusion orinjection molding. In a specific embodiment, the polymer composition isprepared via twin screw extrusion. In the particular context of an opticfiber cable, the polymer composition can be extruded as a jacket for anoptic fiber cable and/or another component. Upon extrusion or injectionmolding, the polymer composition will have either a droplet-dispersedmorphology in which elastomer droplets uniformly disperse in polyolefinmatrix or a co-continuous morphology in which both elastomer andpolyolefin form the continuous phases. Additionally, shear orextensional forces exerting during extrusion or injection moldingaffects the morphology of the polymer composition such that themorphology is elongated to a microfibril (e.g., droplet dispersedmorphology) or extended to a microlayer (e.g., co-continuousmorphology). The resultant morphology primarily depends on thecompatibility and viscoelasticity of the polyolefin and thermoplasticelastomer. Because of the highly directional nature of extrusion andinjection molding, the filler material and elastomer phase will behighly orientated along the extrusion/injection direction and willexhibit anisotropic shapes, i.e., a large amount of microfibrils ormicrolayers are formed and oriented. Because the elastic modulus of thepolyolefin will generally be higher than that of the thermoplasticelastomers, the thermal expansion of the thermoplastic elastomer domainsis restricted by the polyolefin domains. Additionally, the fillermaterial can be selected or engineered to evenly disperse in both thepolyolefin or thermoplastic elastomer phases or selectively localizepredominantly in just one of the phases.

The anisotropy of the resultant phase morphology reduces the CTE in theextrusion direction, which in the case of a cable jacket is along thelongitudinal axis of the cable. In an embodiment, the CTE of the polymercomposition in the extrusion direction is less than 150×10−⁶ m/mK. Inanother embodiment, the CTE of the polymer composition in the extrusiondirection is less than 120×10⁻⁶ m/mK, and in a further embodiment, theCTE of the polymer composition in the extrusion direction is less than100×10⁻⁶ m/mK. In embodiments, the CTE values represent averages takenof measurements of the CTE between −40° C. and 25° C.

As discussed above, the CTE is only one of the two major components ofthermal strain with the other being the elastic modulus. Generally, theaddition of filler materials to a polymer will cause an increase inelastic modulus; however, in the disclosed polymer compositions, theinclusion of the thermoplastic elastomer allows the elastic modulus todecrease or to remain the same despite the inclusion of a filler. In anembodiment, the elastic modulus (alternatively, storage modulus) at −40°C. as measured by dynamic mechanical analysis (DMA) is less than 3000MPa as measured in accordance with ASTM D4065. In a further embodiment,the elastic modulus at −40° C. as measured by DMA is less than 2500 MPa,and in still another embodiment, the elastic modulus at −40° C. asmeasured by DMA is less than 2000 MPa. In a particular embodiment, thethermoplastic elastomer has a low glass transition temperature, such as−20° C. or lower. In another embodiment, the glass transitiontemperature is −40° C. or lower, and in still another embodiment, theglass transition temperature is −60° C. or lower. The low glasstransition temperature allows for the retention of an elongation atbreak of at least 2000/% (as measured by ASTM D638) over the temperaturerange of −40° C. to 80° C., which corresponds to the potential operatingrange of an optic fiber cable. In embodiments, the elongation at breakis at least 400° % over the operating temperature range of an opticfiber cable.

Examples

Several exemplary polymer compositions were made according to theembodiments disclosed herein. In particular, polymer compositions basedon MDPE were developed by mixing MDPE with various thermoplasticelastomers and filler materials. Table 1 discloses the composition andproperties of these exemplary MDPE polymer compositions.

TABLE 1 Formulations and Properties Polymer Compositions E′ CTEElongation at −40° C. (×10⁻⁶ at Break Formulation Weight Ratio (MPa)m/mK) (%) Comparative Examples: 1 MDPE 100/0/0 1969 168.7 >800 2 MDPE/GF80/20 6000 50 6.7 3 MDPE/EPR 70/30 1469 192.8 >800 Examples: 1MDPE/EPR/MMT 60/30/10 1882 167.0 >800 2 MDPE/EPR/WF 60/30/10 2073129.4 >800 3 MDPE/EPR/MMT 50/40/10 1786 126.0 >800 4 MDPE/EVA/WF50/40/10 2354 93.9 >800 5 MDPE/SEBS/MMT 50/40/10 1760 108.2 >800 6MDPE/SEBS/WF 50/40/10 1528 94.9 >800 7 MDPE/SEBS/MMT/WF 47/38/10/5 183098.9 ~600

The elastic moduli of the exemplary compositions were obtained usingDMA. The thermal expansion behavior of the polymer compositions wasmeasured by thermomechanical analysis (TMA) in accordance with ASTME831. In particular, Example 4 of Table 1 was tested using TMA todevelop the graph depicted in FIG. 1. As shown there, a sample ofExample 4 was cycled between −40° C. and 80° C. The first heating cyclewas used to eliminate the thermal history of the sample generated duringprocessing. Thereafter, the CTE in the extrusion direction wascalculated by averaging the CTE over the temperature range of −40° C. to25° C. over multiple cycles. The CTE for each of the exemplaryembodiments of the polymer composition provided in Table 1 weredetermined in this way.

Initially, as can be seen in Table 1, all of the exemplary compositions1-7 exhibited an elongation at break of more than 400%. In particular,even the relatively highly-filled Example 7 (15% filler) was able toachieve an elongation at break of greater than 400%, while stillreducing the CTE in the extrusion direction and slightly decreasing theelastic modulus as compared to MDPE (Comparative Example 1).

In Comparative Example 2, only glass fiber filler material was added tothe MDPE, and as can be seen, the CTE drops from 168×10⁻⁶ m/mK to50×10⁻⁶ m/mK. However, the elastic modulus at −40° C. increases from2000 MPa to 6000 MPa at the same time. Therefore, almost no change inthe overall thermal strain of the polymer composition is provided.

Regarding the polymer compositions according to the present disclosure,the CTE of Example 1 is approximately the same as the controlComparative Example 1, but the elastic modulus is slightly reduced,which overall provides a reduction in thermal strain. In Example 2, itcan be seen that the CTE decreases by 23% while the elastic modulusincreased by only about 5%. The CTE and elastic modulus of Example 3 areboth reduced by 25% and 9%°, respectively. For Example 4, the CTE isdrastically reduced by about 44%, but the elastic modulus is increasedby about 20%. As can be seen when comparing Examples 1-4, the relativeamount of the thermoplastic elastomer and the selection of the fillermaterial and thermoplastic elastomer have an influence on the finalproperties of the polymer composition. Comparing Examples 1 and 2, thesubstitution of MMT with WF produced a significant reduction in the CTE.Comparing Examples 1 and 3, the inclusion of 10% more EPR (thermoplasticelastomer) by weight also provided a significant reduction in the CTE aswell as the elastic modulus. Additionally, Examples 1 and 4 demonstratethat WF can provide significant reductions in CTE with only modestincreases in elastic modulus.

Turning to Example 5, the CTE is reduced by about 36% with anaccompanying reduction of elastic modulus of about 11%. In Example 6,the CTE is reduced by almost 44%, and the elastic modulus is reduced bymore than 22%. In Example 7, a combination of filler materials is used.Specifically, in Example 7, the 10% by weight of MMT and 5% by weight ofWF were added to the MDPE and SEBS. As mentioned above, despite therelatively high amount of filler material, Example 7 provides a 41%reduction in CTE and a 7% reduction in elastic modulus. In embodimentsof the polymer composition adapted for low temperature applications,SEBS is chosen as the thermoplastic elastomer because its butadiene softblocks typically have a low glass transition temperature of −90° C. Thelow glass transition temperature helps to ensure that the elasticmodulus remains the same at cold temperature.

The exemplary polymer compositions were also analyzed using a scanningelectron microscope (SEM). FIG. 2A shows an SEM micrograph of Example 1viewed perpendicular to the cable axial direction. FIG. 2B shows an SEMmicrograph of the same polymer composition viewed parallel to the cableaxial direction. As can be seen in FIGS. 2A and 2B, the MMT particles(the white flecks in the micrograph) are well dispersed in thesub-micrometer scale with few agglomerates that are larger than 10 μm.In comparing FIGS. 2A and 2B, it can be seen that there is a differencein orientation and length of MMT particles along the two directions. MMTparticles in the parallel direction shown in FIG. 2B are longer andbetter aligned than those in the perpendicular direction shown in FIG.2A. The anisotropy of the MMT particles stems from the elongationalforce (e.g., from extrusion and drawing-down) that was applied duringmelting processing.

The polymer compositions shown in FIG. 2B was further etched by solventto remove the thermoplastic elastomer domains. The etched parallelsurface of FIG. 2B is shown in FIGS. 3A and 3B, with FIG. 3B being twicethe magnification of FIG. 3A. In FIGS. 3A and 3B, the blank areas shownin the SEM micrographs of the etched surface correspond to thethermoplastic elastomer domains. As can be seen, the thermoplasticelastomer domains are elongated in the extruded direction (denoted bythe arrow in the upper lefthand corner of the micrograph) and deformedinto microfibrils or microlayers, i.e., the polymer composition exhibitsan anisotropic, co-continuous phase morphology. As discussed above, theanisotropy contributes to the lowering of the polymer composition's CTEin the extrusion direction; however, the overall bulk CTE will remainthe same (which means that the CTE in the radial directionsperpendicular to the extrusion direction will increase).

Additionally, the exemplary polymer compositions were tested todetermine the thermal contraction stress. Testing was performed usingDMA in the temperature range of 35° C. to −40° C. according to ASTMD4065. Specifically, extruded samples having a thickness of 2 mm werecooled from 35° C. to −40° C. at a rate of 1.0° C. per minute. Thesamples were then held at −40° C. for sixty minutes. For ComparativeExample 1 (MDPE), the thermal contraction stress was measured to be 7.6MPa. For the exemplary polymer compositions disclosed herein, thethermal contraction stress was less than 3.0 MPa.

The polymer composition disclosed herein can be applied in a variety ofcontexts. In a particular embodiment shown in FIG. 4, the polymercomposition is used as a jacket for a cable or cable component. Thecable shown in FIG. 4 is a fiber optic cable 20. Cable 20 includes acable body, shown as cable jacket 22, having an inner surface 24 thatdefines a channel, shown as central bore 26. Pluralities ofcommunication elements, shown as optical fibers 28, are located withinbore 26. The cable 20 includes a plurality of core elements locatedwithin central bore 26. A first type of core element is an opticaltransmission core element, and these core elements include bundles ofoptical fibers 28 that are located within tubes, shown as buffer tubes30. Buffer tubes 30 are arranged around a central support, shown ascentral strength member 34. Central strength member 34 includes an outercoating layer 36. A barrier material, such as water barrier 38, islocated around the wrapped buffer tubes 30. An easy access structure,shown as rip cord 39, may be located inside cable jacket 22 tofacilitate access to buffer tubes 30.

In one embodiment, the polymer composition is incorporated into thecable jacket 22 of fiber optic cable 20. In another embodiment, thepolymer composition is used to upcoat the central strength member 34 toform the outer coating layer 36. For example, the selection of thenumber of buffer tubes 30 can define an interior open geometry that isfilled/supported by the central strength member 34 and outer coatinglayer 36. In order to reduce the cost of the optic fiber cable 20, thecentral strength member 34 can be made as thin as possible while stillproviding the necessary support for the cable 20. The remainder of theinterior open geometry can be filled with the outer coating layer 36 byupcoating the polymer composition on the central strength member 34. Inthis way, the cost of providing the central strength member 34 and outercoating layer 36 is reduced as the presently disclosed polymercomposition used to form the outer coating layer 36 is generally lessexpensive in terms of material cost than the central strength member 34.

Also, using the polymer composition disclosed herein provides severaladvantages. In particular, the polymer composition can be used toproduce optic fiber cables with enhanced thermal performance and reducedmanufacturing cost. Ultimately, incorporating the disclosed polymercomposition in various components of the optic fiber cables can help torealize the goals of reducing buffer tube size, shortening lay lengths,and driving cable design to concurrent performance limits under load andat low temperature. Further, in contrast to certain polymer compositionsthat, in some circumstances, may have a relatively low elongation atbreak throughout the operating temperature range and that produce arigid jacket likely to crack under impact, bending, and/or twistingstresses at low temperatures, the presently disclosed polymercomposition can help to produce an optical cable with significantlyimproved temperature cycling performance. Also, in contrast to certainlow-CTE polymer compositions that contain a high amount of filler, thepolymer compositions made according to the present disclosure do nothave a high modulus, poor toughness, or poor appearance, nor are thepresently disclosed polymer compositions difficult to process based on ahigh filler content.

Further, polymer compositions made according to the embodimentsdisclosed herein offer several additional advantages when used ascomponents for optic fiber cable. For example, the polymer compositioncan help expand the optical fiber cable operating temperature range to−40° C. or below. Also, the lower thermal contraction stress of lessthan 3.0 MPa can reduce the attenuation of optic fibers in contact withthe polymer composition that results from the contraction of the polymercomposition in cold environments. Additionally, the polymer compositioncan allow for smaller buffer tubes to be used, resulting in lowermaterial cost and lower overall product cost. As discussed above, thepolymer composition can help to reduce the diameter (and consequentlythe cost) of the central strength member. Further, because of thepotential to produce smaller cable sizes by using the disclosed polymercomposition, the resultant cable is expected to have better blowingperformance during installation. In another embodiment, a cable having ajacket made of the disclosed polymeric composition can also include anadditional outer layer of LLDPE, MDPE, HDPE, etc. to lower thecoefficient of friction of the resulting cable when the cable is blowninside a duct. In such embodiments, the outer layer can be thinner thanthe cable jacket.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred. In addition, as used herein, thearticle “a” is intended to include one or more than one component orelement, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosed embodiments. Since modifications,combinations, sub-combinations and variations of the disclosedembodiments incorporating the spirit and substance of the embodimentsmay occur to persons skilled in the art, the disclosed embodimentsshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A polymer composition comprising: a polyolefin;and at least 30% by weight of a thermoplastic elastomer; wherein thepolymer composition has an elastic modulus of less than 2000 MPa asmeasured using dynamic mechanical analysis (ASTM D4065), an elongationat break of greater than 200% along the longitudinal axis (measuredaccording to ASTM D638), and a thermal contraction stress of less than3.0 MPa as measured using dynamic mechanical analysis.
 2. The polymercomposition of claim 1, wherein the polyolefin is selected from thegroup consisting of medium-density polyethylene, high-densitypolyethylene, low-density polyethylene, linear low-density polyethylene,polypropylene, and combinations thereof.
 3. The polymer composition ofclaim 1, comprising less than 60% by weight of the thermoplasticelastomer.
 4. The polymer composition of claim 1, wherein thethermoplastic elastomer is selected from the group consisting ofethylene-propylene rubber, ethylene-propylene-diene rubber,ethylene-octene, ethylene-hexene, ethylene-butene, ethylene-vinylacetate, styrene-ethylene-butadiene-styrene, thermoplastic vulcanizates,polyolefin elastomers, ethylene/alpha-olefin copolymers, andcombinations thereof.
 5. The polymer composition of claim 1, wherein thethermoplastic elastomer has a shear viscosity that is lower than orequal to the shear viscosity of the polyolefin when measured at 200° C.and 100 s⁻¹.
 6. The polymer composition of claim 1, further comprisingless than 30% by weight of a filler material.
 7. The polymer compositionof claim 6, wherein the filler material is selected from the groupconsisting of mica, talc, montmorillonite, kaolinite, bentonite,synthetic clay, and combinations thereof.
 8. The polymer composition ofclaim 6, wherein the filler material is selected from the groupconsisting of wood flour, glass fiber, halloysite, wollastonite,magnesium oxysulfate, and combinations thereof.
 9. The polymercomposition of claim 1, wherein the thermoplastic elastomer has a glasstransition temperature that is less than −20° C.
 10. The polymercomposition of claim 1, comprising up to 1% of a low friction additiveselected from the group consisting of a fatty acid, fatty acid amide,and combinations thereof.
 11. An extruded polymer article, the polymerarticle having a longitudinal axis generally in the direction ofextrusion, the polymer article comprising: a polymer composition,comprising: a polyolefin; and at least 30% by weight of a thermoplasticelastomer; wherein the polymer composition has an elastic modulus ofless than 2000 MPa and a thermal contraction stress of less than 3.0 MPaas measured using dynamic mechanical analysis (ASTM D4065).
 12. Theextruded polymer article of claim 11, wherein the extruded polymerarticle is a jacket for a cable and the longitudinal axis is along thelength of the cable.
 13. The extruded polymer article of claim 11,wherein the extruded polymer article is an outer coating layer of acentral strength member of a fiber optic cable.
 14. A cable comprising:at least one communication element; a polymeric jacket that surroundsthe at least one communication element; wherein the polymeric jacket isformed at least in part from a polymer composition comprising: apolyolefin; and at least 30% by weight of a thermoplastic elastomer;wherein the polymer composition is extruded to form the polymericjacket, the polymeric jacket defining a longitudinal axis generally inthe direction of extrusion; wherein the polymer composition has anelastic modulus of less than 2000 MPa and a thermal contraction stressof less than 3.0 MPa as measured using dynamic mechanical analysis (ASTMD4065).
 15. The cable of claim 14, wherein the at least onecommunication element comprises an optical fiber.
 16. The cable of claim14, further comprising: a central strength member that runs along atleast a portion of a length of the cable; wherein the central strengthmember includes a coating of the polymer composition along the length ofthe central strength member.
 17. The cable of claim 14, wherein a CTE ina radial direction is greater than the CTE along the longitudinal axis.18. The cable of claim 14, wherein the polymeric jacket is coextrudedwith an outer layer of a material selected from the group consisting oflinear low-density polyethylene, medium-density polyethylene,high-density polyelthylene, and combinations thereof, and wherein theouter layer is thinner than the polymeric jacket.